1. Field of the Invention
The present invention relates generally to blades used for example in turbomachinery, and particularly to an improved turbine rotor blade.
2. Description of the Related Art
A gap between the rotor and the casing exists in all turbomachinery such as gas turbine engines, compressors, radial compressors or pumps. Furthermore, the minimum size of this gap is dictated by different rates of thermal expansion and radial growth of the blades and the casing during different operational conditions. It is well established that greater operating efficiency and power output of a turbomachine may be achieved by any means reducing the tip leakage flow, controlling the boundary layer, and increasing inlet operation temperatures.
The tip leakage flow is the largest single source of energy loss in a turbomachine. The interaction of leakage flow, blade, and annulus wall boundary layers and radial transport of mass, momentum and energy results in a highly complex flow field near the tip region of a turbomachine.
In order to reduce the tip leakage flow several ideas have been used, such as the cutting of grooves, squellers, or the use of abrasive materials applied either on the blade tip or on the casing, in order to obtain the smallest possible clearance and thereby reduce the leakage flow by increasing the flow resistance in the tip region from the pressure to the suction side. Such structures are described in greater detail in U.S. Pat. Nos. 4,589,823 and 4,571,937.
A further idea to reduce the tip leakage flow is the so called active clearance control. Thereby, the clearance or gap between the tip of the rotor blade and the casing of a turbine engine is maintained at a minimum by cooling or heating the casing of the turbine engine.
Furthermore, other problems exist:
The high temperatures downstream of the combustion chamber in a gas turbine require cooled rotor blades due to material constraints. The structures providing cooling for the turbine blades have generally a cooling fluid entrance at the root of the blade structure and exhaust exits located at the trailing edge, leading edge and at the tip plane of the blade. These exhaust exits are used to get rid of the cooling fluid or to produce a film of cooling air as in U.S. Pat. Nos. 4,601,638. Hill, Liang, and Auxier in U.S. Pat. No. 4,601,638 teach the use of air holes to provide cooling, the air holes having axes which run parallel to the plane of the blade tip. Further structures are described in greater detail in U.S. Pat. Nos. 4,424,001, 4, 540,339 and 4,606,701.
According to U.S. Pat. No. 4,540,339, for example, a cooling fluid flows through openings arranged in the tip surface of the blade and is directed against the tip side wall surfaces in a plane perpendicular to the side walls.
In U.S. Pat. No. 4,040,767 a coolable nozzle guide vane in the turbine section of a gas turbine engine is disclosed. Cooling air flows out of orifices in the blade side walls and the blade root and is distributed about the walls of the sections which are in contact with the hot working gases flowing through the turbine during operation of the engine.
All these purposes provide cooling of the rotor blade and other sections. However, they do not influence or reduce the tip leakage flow and the corner separation zones.
An object of the invention is an improved configuration for a blade, especially a rotor blade in a turbine engine, by which the energy loss in the turbine engine is significantly reduced.
A further object of the invention is to reduce the tip leakage flow and to influence the complex flow field, thereby to reduce the corner separation zones and the energy losses produced by the complex flow field along the rotor blade.
Yet another object of the present invention is to cool the surfaces of the rotor blade, and its root.